Part Load Instability and Rotating Stall in a Multistage Low Specific Speed Pump

The behaviour of the relative flow in centrifugal turbomachines is extremely complex due to the existence of various fluid dynamic phenomena and their interaction. At design and off-design operating conditions, the relative flow is subject to stationary unsteadiness which includes flow separation and wakes associated with passage pressure gradients, secondary flows, and boundary layer stability. It may also be subject to periodic unsteadiness such as is the rotating stall and cyclic flow phenomena induced by the casing. This paper describes detailed measurements of the relative velocity field in a very low specific speed centrifugal pump impeller (Ns=515). Measurements were conducted by means of a recently developed rotating laser-Doppler anemometry system. Detailed quantitative description of the mean and fluctuating components of the primary and secondary velocity fields are presented for an impeller without volute at design, 50% design and shut-off conditions. The flow pattern in this low specific speed impeller with high blade loading is dominated by the relative eddy (a phenomenon also present in potential flow) which has suppressed suction side separation. When the impeller was fitted with a volute, the cyclic variation of the impeller exit flow, induced by the volute at low flow rates, is also presented.

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Discussion: “Rotating Stall Induced in Vaneless Diffusers of Very Low Specific Speed Centrifugal Blowers” (Kinoshita, Y., and Senoo, Y., 1985, ASME J. Eng. Gas Turbines Power, 107, pp. 514–519)

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.3239762 ◽

1985 ◽

Vol 107 (2) ◽

pp. 519-520 ◽

Cited By ~ 1

Author(s):

R. Van den Braembussche

Keyword(s):

Gas Turbines ◽

Rotating Stall ◽

Low Specific Speed ◽

Specific Speed ◽

Vaneless Diffusers

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Rotating Stall Induced in Vaneless Diffusers of Very Low Specific Speed Centrifugal Blowers

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.3239761 ◽

1985 ◽

Vol 107 (2) ◽

pp. 514-519 ◽

Cited By ~ 28

Author(s):

Y. Kinoshita ◽

Y. Senoo

Keyword(s):

Flow Analysis ◽

Rotating Stall ◽

Experimental Results ◽

Flow Coefficient ◽

Critical Flow ◽

Flow Rates ◽

Small Flow ◽

Low Specific Speed ◽

Specific Speed ◽

Vaneless Diffusers

The limit of rotating stall was experimentally determined for three very small specific speed centrifugal blowers. The impellers were specially designed for stall-free at very small flow rates, so that the cause of rotating stall could be attributed to the vaneless diffusers. Experimental results demonstrated that the blowers did not stall until the flow coefficient was reduced to very small values, which had never been reported in the literature. The critical flow coefficient for rotating stall agreed very well with the prediction based on a flow analysis and a criterion for rotating stall in vaneless diffusers developed by the authors.

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Investigation of the Flow Instabilities of a Low Specific Speed Pump-Turbine: Part 1 — Experimental and Numerical Analysis

Volume 1: Fluid Applications and Systems; Fluid Measurement and Instrumentation ◽

10.1115/fedsm2020-20268 ◽

2020 ◽

Author(s):

Sabri Deniz ◽

Armando Del Rio ◽

Martin von Burg ◽

Manuel Tiefenthaler

Keyword(s):

Experimental Data ◽

Guide Vane ◽

Turbulence Models ◽

Operating Mode ◽

Rotating Stall ◽

Flow Instabilities ◽

Pump Turbine ◽

Flow Features ◽

Low Specific Speed ◽

Specific Speed

Abstract This is the first part of a two-part paper focusing on the flow instabilities of low-specific pump turbines. In this part, results of the CFD simulations and experiments of the research carried out on a low specific speed model pump-turbine at HSLU (Lucerne University of Applied Sciences) Switzerland are presented. The requirements of a stable and reliable pump-turbine operation under continuously expanding operating ranges, challenges the hydraulic design and requires new developments. Previous research at the HSLU [1] analyzed the instabilities of a medium specific speed (i.e. nq = 45) pump turbine. This paper presents the results of experimental (model pump-turbine at the test rig) and numerical (CFD) investigations of the pump-turbine instabilities of a low specific speed (nq = 25) pump-turbine in the turbine operating mode in the region of S-shaped characteristics (that is where the pump-turbine is synchronized and oscillations may occur during load rejection). The four-quadrant characteristics of a low specific speed model pump-turbine with two similar runners differentiating in the size (diameter) are measured. Testing of both runners with the same guide vane system provided information about the effects of the increased vaneless space (the distance between the guide vanes and runner) on the pump-turbine performance and stability both in turbine- and pump operating modes. A CFD methodology by using different numerical approaches and applying several turbulence models is developed in order to accurately predicting the characteristics of the reversible pump-turbines in the S-shaped region (speed no load conditions) as well as analyzing the flow features especially at off-design conditions. This CFD model is validated against the experimental data at 6° and 18° guide vane openings in turbine operating mode. With the measured data of the unsteady pressure measurements and detailed investigation of unstable ranges on the pump-turbine characteristics, flow instabilities in the low-specific speed model pump-turbine are analyzed. Relevant frequencies such as rotating stall, steady and unsteady vortex formations are determined. Based on the analysis of the experimental data and CFD results focusing especially on the flow features in the vaneless space and at the runner inlet, the onset and development of the flow instabilities are explored.

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A Behavior of the Diffuser Rotating Stall in a Low Specific Speed Mixed-Flow Pump

International Journal of Fluid Machinery and Systems ◽

10.5293/ijfms.2009.2.1.031 ◽

2009 ◽

Vol 2 (1) ◽

pp. 31-39 ◽

Cited By ~ 8

Author(s):

Masahiro Miyabe ◽

Akinori Furukawa ◽

Hideaki Maeda ◽

Isamu Umeki ◽

Yoshinori Jittani

Keyword(s):

Rotating Stall ◽

Mixed Flow ◽

Low Specific Speed ◽

Specific Speed ◽

Flow Pump

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Part Load Instability and Rotating Stall in a Multistage Low Specific Speed Pump

Volume 1: Fluid Applications and Systems; Fluid Measurement and Instrumentation ◽

10.1115/fedsm2020-20086 ◽

2020 ◽

Author(s):

E. M. A. Vermunt ◽

K. A. J. Bruurs ◽

M. S. van der Schoot ◽

B. P. M. van Esch

Keyword(s):

Flow Rate ◽

Head Loss ◽

Rotating Stall ◽

Critical Flow ◽

Flow Rates ◽

Critical Flow Rate ◽

Lower Flow ◽

Low Specific Speed ◽

Saddle Type ◽

Specific Speed

Abstract A new diffuser design is developed for a low specific speed, multistage pump. In this design the diffuser and the de-swirl vanes are integrated into single vanes. This creates diffuser channels that extend from behind the impeller exit through the cross-over, up to the eye of the next stage impeller. Experiments show the occurrence of a saddle type instability in the head curve. At a critical flow rate of close to 50% of the flow rate at Best Efficiency Point (BEP), the head drops by 7% of the head at BEP. In this study Computational Fluid Dynamics (CFD) are used in an effort to understand the underlying flow phenomena. The head curve that is obtained with the transient CFD simulations contains a saddle type instability at a flow rate that is approximately the same as in the experiments, but with a lower magnitude. At flow rates higher than the critical flow rate, the predicted head and power are in very good agreement with the experimental data. At flow rates lower than the critical flow rate, the head and power are slightly over-predicted. An analysis of the pressure distribution in the pump reveals that the head loss at different flow rates in the diffuser shows a discontinuity at the critical flow rate. Since both the impeller head and the head loss in the vaneless gap increase continuously for decreasing flow rate, this is an indication that the cause of the head instability lies in the diffuser. Moreover, a strong increase in the variability of head and power at flow rates below the critical flow suggests that the phenomenon is unsteady. Flow patterns in the impeller and in the diffuser, as calculated by CFD, show a high degree of periodicity and are very similar for flow rates down to the critical flow rate. However, for lower flow rates the flow pattern changes completely. A single rotating stall cell is observed that causes two or three neighboring diffuser channels to stall, leading to a significantly lower flow rate or even a reversed flow. This stall pattern rotates in the direction of impeller rotation at a very low frequency of approximately 3.3% of the impeller rotation frequency.

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Numerical Simulation of Low Specific Speed American Petroleum Institute Pumps in Part-Load Operation and Comparison With Test Rig Results

Journal of Fluids Engineering ◽

10.1115/1.4005769 ◽

2012 ◽

Vol 134 (2) ◽

Cited By ~ 18

Author(s):

Helmut Benigni ◽

Helmut Jaberg ◽

Hoi Yeung ◽

Tony Salisbury ◽

Owen Berry ◽

...

Keyword(s):

Numerical Simulation ◽

American Petroleum Institute ◽

Test Rig ◽

Histogram Method ◽

Part Load ◽

Adaptive Simulation ◽

Computational Fluid Dynamics Cfd ◽

Low Specific Speed ◽

Specific Speed ◽

Valve Operation

A low specific speed centrifugal pump is investigated by means of numerical simulation, especially in deep part-load operation. The 3D computational fluid dynamics (CFD) model includes the front and back cavities, a 360 deg impeller and a double volute, as well as suction and pressure pipes. Stationary calculations show a strong clocking effect and lead to an overprediction of the head close to zero flow rate. A one-dimensional estimation of the head at the closed valve operation point is compared to the 3D CFD results and also a series of test rig results. In a second step, the whole head curve is calculated by a fully transient calculation using the shear stress transport–scale-adaptive simulation (SST–SAS) turbulence model. For the net positive suction head (NPSH) estimation, the histogram method is applied providing good correlation to the test rig measurement—as do the head curve and the efficiency.

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Four-quadrant Characterization of Hydrodynamic Phenomena in a Low Specific Speed Centrifugal Pump

Ingenieria y Universidad ◽

10.11144/javeriana.iued25.fchp ◽

2021 ◽

Vol 25 ◽

Author(s):

Hernan Dario Bolaños ◽

Francisco Botero

Keyword(s):

Centrifugal Pump ◽

Classical Method ◽

Characteristic Curve ◽

Frequency Domain Analysis ◽

Rotating Stall ◽

Low Specific Speed ◽

Specific Speed ◽

Four Quadrant

Objective: Identify and characterize subsynchronous hydrodynamics phenomena in a low specific speed centrifugal pump based on its four-quadrant characteristic curve. Materials: A 1.5 HP ITT Goulds pump instrumented with pressure transductors, an accelerometer, a torque sensor and a tachometer. Flow rate measurement was done with an ultrasonic transit time clamp-on flow meter. Methods: Time and frequency domain analysis with phase analysis were used to identify spectral components linked to hydrodynamic phenomena such as rotating stall and surge. Results and discussion: This work approaches an alternative method to calculate the phase angle using pressure signals without filtering. Related with hydrodynamic phenomena, the evidence collected suggests the presence of rotating stall in some operation points of the four-quadrant characteristic curve. Furthermore, in the third quadrant, rotating stall coexist with surge. Conclusions: The instrumentation and methods regarded in this work allow to collect evidence to identify in-phase and out of phase subsynchronous hydrodynamic phenomena. The classic cross-correlation-based method was improved to ease the diagnosis of subsynchronous phenomena by visual inspection. A new quantitative approach was introduced to detect subsynchronous phenomena, based on the Fourier analysis; it was validated with a case study for which the classical method was not suitable.

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